The field of the present disclosure relates to optical readers and more particularly, to methods and systems for using and generating virtual scan lines for imaging of encoded symbols.
Optical reading of data or encoded symbols, such as barcode labels, has been used for some time in many applications. Typically, a barcode consists of a series of parallel light and dark rectangle areas of varying widths. Different widths of bars and spaces define different characters in a particular barcode symbology. A barcode label may be read by a scanner which detects reflected and/or refracted light from the bars and spaces comprising the characters. One common method of reading the barcode label is by scanning a beam of light (e.g. a laser beam) across the barcode label and detecting the reflected light via an optical detector. The detector generates an electrical signal having an amplitude determined by the intensity of the collected light.
Scanning laser barcode reading systems may either have a single scan line directed toward the target, as in the case of typical handheld barcode readers, or may have a pattern of laser scan lines, which is typically the case for fixed mounted barcode readers. Another method of reading a barcode label involves illuminating the barcode label with a light source and detecting the reflected light through an imaging lens onto an array of optical detectors connected to an analog shift register, such as a charge coupled device (CCD) or CMOS sensor. This detector may be a one dimensional line of pixels (a so-called linear imager) or a two dimensional array of pixels (a so-called area sensor). An electrical signal is generated having an amplitude determined by the intensity of the collected light. As the image is read out, positive and negative transitions in the electrical signal occur signifying transitions between the bars and spaces.
The scan patterns of fixed mounted barcode readers impose limitations on the ability to read highly truncated or damaged barcodes. These limitations are overcome by area imaging readers, as the redundant information contained in the full height of the bars and spaces can be used to discern the bar and space pattern versus a single strike through the barcode that occurs in a fixed mounted laser reader. However, imaging readers have disadvantages when used in high speed applications. There is a tradeoff of illumination intensity, depth of field, and image capture speed that limits the overall performance of such barcode readers, due to the signal to noise limits of the image sensor. Improvement of depth of field in high speed imaging readers is typically accomplished by increasing the illumination intensity, as the other factors, such as imager noise and lens aperture have more significant side effects in their optimization.
The present inventors have recognized a need for improved systems and methods for reading optical codes using a high speed imaging system.